1. Field of Invention
This invention relates to devices that are used to separate solid materials having some differing physical characteristic, e.g., density, especially to those devices which separate respective different divided solids having some corresponding different physical characteristic when suspended in a transporting fluid under the influence of centrifugal force disposed within a containment (a vortex body) transporting the fluid between inlet(s) and outlet(s).
2. Description of Prior Art
Numerous methods have been employed for separating divided solids suspended in moving fluids (fluid streams). Many methods take advantage of the hydrostatic forces acting on buoyant solids when placed in a liquid medium. This "buoyant" force can be imparted by natal gravitational force or by centrifugal force. In general, the methods that employ centrifugal force have higher throughput rates and/or perform more accurate separations than those that rely on gravity alone.
Some devices that separate solids by the use of centrifugal force use motors or other physical means of supplying energy to impart a centrifugal motion to the fluid. Devices of this sort have traditionally been referred to as "centrifuges", a typical example of which is described by Brandrup et al. These devices are, in general, effective at separating solids, however they usually have many moving parts, and therefore are subject to mechanical failure and require routine maintenance. They are also usually difficult to manufacture and therefore expensive.
Many devices that separate solids by the use of centrifugal force consist of a stationary cylindrical or conical body into which a moving slurry of a liquid medium having divided solids (solid particles) suspended therein is admitted or introduced. The moving slurry may be brought in to a separating (vortex) body through a fluid entrance or inlet from a container at a higher elevation, taking advantage of the pressure `head` or be introduced from a source driven by a pump.
The fluid inlet may be oriented tangentially to the vortex axis of the separator body, so the momentum of the inlet fluid imparts or adds to a rotational flow to the rotating fluid contained in the device The oldest and most traditional of these devices is called a hydrocyclone. The first hydrocyclone was described by U.S. Pat. No. 453,105 to Bretney. Although the hydrocyclone was originally patented for the use of removing water from dense solids ("dewatering`), the fundamental shape of the device has stayed the same. Hydrocyclones were first applied to the separation of solids in the field of "coal benefaction", and one of the first patents for this application was awarded by U.K. Patent 528,590 to the Directie van de Staatsmijnen.
Hydrocyclones have high throughput rates, require very little maintenance, and are inexpensive to construct and operate. However, they do not effectively separate solids that have small differences in density. This is due to the fact that a substantial amount of turbulence is generated inside the hydrocyclone. This turbulence is primarily due to the fact that the two exit ports are at different (opposing) ends of the device.
To understand why exit ports at different ends of the device negatively affect the separation, it is useful to analyze the flow inside a device in terms of its directional components. Using the parlance of cylindrical coordinate systems, these components are angular (or "rotational"), radial, and axial with respect to an axis defining the circulating fluid (the vortex). The centrifugal forces that separate particles from each other are imparted by the rotational component of the flow field, but the other components of flow, the radial and axial, tend to disrupt the separating effects of the rotational flow. Devices that have the two outlet ports at different ends of the device generate excessive radial and axial flows that disrupt the separating effects imparted by the rotational component of the flow.
Numerous other variations of the hydrocyclone have been invented. For example, U.S. Pat. No. 3,802,570 to Dehne claims a novel exit port and U.S. Pat. No. 4,838,434 to Miller et al claims an air-sparged hydrocyclone. (An "air-sparged" hydrocyclone is one with a fritted porous wall through which compressed air is injected. The air typically aids in separating "fines" from coarse particles or hydrophobic particles form hydrophilic particles.) However, all of the hydrocyclone variations still incorporate exit ports that are on opposite ends of the device.
Other devices have been used for separating particles in a liquid medium. One of the more useful is referred to as the "Dyna-Whirlpool" separator, described by Goldberger and Robbins (1984). This device is predominantly cylindrical and has both an entrance port and an exit port at both ends of the device. A liquid feed enters at one end and a slurry feed at the other. The separated particles exit from tangential and axial ports at opposite ends of the device. This device is similar in principal to a hydrocyclone but is more complicated to operate because two streams need to be supplied to the unit, and therefore two pumps need to be employed.
There are a few patents that describe devices having both outlet ports on the same end. A first is U.K. Patent 537,771 by Alexander in 1940 "Improvements in Centrifugal Separators for Extracting Solids from Liquids" (the Alexander patent). Alexander distinguishes his improved centrifugal separator (FIGS. 1-6) from the then existing prior art separator devices which have fluid inlet (`admission`) and fluid outlet (`discharge`) at the same one end of the `vortex` chamber. In column 1 lines 48-57 he describes the improved separator as having:
"the inlet (reference number 7 in the Figures) is at or near the circumference at one end and the outlet (reference number 4) is of less diameter and centrally situated, or nearly so, at the other end of the vortex. The said inlet being of single or multiple tangential type, or vaned or vaneless type, and the said outlet being of plan circular or annular section and the flow in which is in a direction away from the inlet"
Alexander thus shows and describes one or more inlets 7 at one end of the "vortex" separating chamber and a single fluid outlet 4 at the other. The inlets 7 are shown having inlet steam(s) directed along various orientations with respect to the vortex axis; e.g., tangential to the chamber outer circumference and perpendicular, oblique or askew to the vortex axis, or parallel to or coaxial with the vortex axis.
Alexander also shows a closed "receptacle or hopper" 8 situated in spaced apart relationship to the inlet(s) in FIGS. 1, 4, 5, and 6. The `hopper` 8 is described as positioned so that it "receives the extracted comparatively dense material." (columns 3, line 33, 34). The hopper 8 is shown variously as parallel to the outlet axis or coaxial therewith at the same end of the `vortex chamber` as the outlet. Alternatively the hopper is shown at right angles to the chamber vortex axis and also perpendicular to either or both the inlet and outlet.
Alexander's claim 1 refers to "an admission passage or passages for admitting the liquid with a tangential component of motion to the vortical chamber" and "another passage or passages--through which the said extracted material is transferred to the receptacle;" (column 4, lines 118-124).
Thus it is clear that Alexander's device is restricted to separators with a single fluid outlet that provides a single outlet stream. Also the separators of Alexander's patent are not restricted to having tangential inlets, but include inward projecting inclined vanes for producing `vortical` separator flow.
Alexander's devices, it is clear, were designed and patented specifically for the application of removing solids from a single liquid stream (i.e. "dewatering") and depositing them in a fixed, closed receptacle while directing the liquid to be discharged at a single exit or port.
Alexander's devices would not facilitate separating two (or more) suspended solids (divided particles) from each other, as there is only one receptacle and one outlet stream. Another separator device is described in U.S. Pat. No. 5,224,604 by Duczmal et al. (Duczmal) Duczmal is concerned with improvements in separator devices combining multiple forces: centrifugal force, Fc (vortex, e.g., hydrocyclone effects), magnetic repelling force, Fr (on diamagnetic particles) , and hydrostatic force, Fh, i.e., the flotation effect on air-bubble/particle aggregates, specifically for hydrophobic particulates.
Duczmal's devices develop a radial distribution of particles suspended in fluid flowing in the vessel by the combined hydrostatic, magnetic and centrifugal forces. Separation of particles from the distribution is enhanced by a "stream splitter" (column 10, line 55) capturing different portions of the swirling fluid in the vessel taking advantage of different combinations of forces causing particles of different characteristics to move in different directions.
Embodiments of the Duczmal patent show a predominately circular hydrocyclone vessel with fluid inlet at one end and fluid outlet or outlets at the opposed end. All of the embodiments of the Duczmal disclosure have at least one of the exit outlets configured as an annular exit opening i.e., disposed around the complete circumference of the vessel at or near the exit end of the vessel. The annular exit opening discharges a portion or all of the exit fluid in an unconstrained manner open to the environment, e.g., as an "outward splayed fluid stream" column 8, line 48.
The outward splayed exit fluid sprays substantially radially from the axis of the unit. This feature is disadvantageous for several reasons:
(a) The fluid exiting the device typically must be caught by a tank or trough that would take up considerable floor space and would tend to require extra time and labor to maintain or be unsafe, in the case where the exit fluids contain harmful or undesirable materials, e.g., sewage. PA1 (b) the fact that the fluid exits directly to the atmosphere limits the exit pressure and consequently limits the fluid pressure distribution within a hydrocyclone vessel of a given size (and therefore limits fluid rotational speed) inside the device and thus separation efficiency: recovered mass per unit energy expended, PA1 (c) If the exiting fluid needed to be transported to a different location at higher elevation than the discharge level, another pump would have to be employed, whereas with a constrained, i.e., sealed exit port, the exiting fluid passing downstream from the separating exit could retain sufficient pressure to move the downstream fluid through a coupled pipe to another location or as an input to a following device such as another separator. PA1 (a) Separators having outlets at different ends of the device, tend to cause excess turbulence (i.e., energy loss) from directing the fluid flow in opposing directions, and lessened efficiency in transferring motional energy from the input stream to the rotational separating forces in the separating chamber or body. This turbulence not only results in reduced separation efficiency, but it also leads to excess differential pressure loss along the separation body thus higher inlet pressure required to pump fluid at a given rate through the device. PA1 (b) Dividing the inlet fluid flow toward two or more widely separated exits causes excess friction loss for a given volume flow rate: e.g., for a single inlet flow of a given volume flow rate directed into a channel or channels with widely separated exit ports causes extra friction loss along the external channel walls between the spaced apart exit ports. PA1 (c) In the case of conical devices, their manufacture can be expensive due to the fact that unique casting molds have to be manufactured. PA1 (d) Devices that do have two spaced apart passages for receiving fluid or solid material from the separating fluid stream have either not allowed for two spaced apart exit fluid streams or have at least one exit port that allows unconstrained exit fluid flow thus potentially wasting fluid energy and/or prohibiting retention of fluid energy for subsequent use. PA1 discharge (exit) ports for exit fluid flow disposed at or adjacent to one another on one end of a vortex separating body; PA1 an inlet port(s) disposed at one end of a separating body having discharge (exit) ports for exit fluid flow disposed at or adjacent to one another at an opposite end of the separating body; PA1 increased separation efficiency; solid mass separated per unit energy expended. PA1 a body that is predominantly cylindrical in shape that can be made inexpensively from standard sizes of pipe or tubing. PA1 a device that is predominantly cylindrical in shape so that the separation (vortex) length of the device can be changed simply by installing or removing sections of pipe or tubing. PA1 a device which promotes smooth rotational flow within the vortex region, therefore affecting an efficient separation of particles carried by the transporting fluid therein and reducing the pressure and/or energy required to move the fluid through the device. PA1 a device with entrance and especially with exit ports that are predominantly closed to the atmosphere so that exit fluid can be cleanly and efficiently transported from the device to a subsequent location or an additional device, especially another separator.
Additionally, the Duczmal patent deals specifically with devices that impart electrical charges to the particles or that use magnetic fields to aid in the separation of the particles.
In summary, all of the stationary prior art separation devices disclosed suffer from at least one of the following deficiencies: